Process for the manufacture of driver bits

ABSTRACT

A greatly strengthened driver bit is formed having a &#39;&#39;&#39;&#39;pearshaped&#39;&#39;&#39;&#39; cross-section and a grain structure that conforms to the external bit configuration. The driver bit is initially formed by hot-forging in an impact press; pre-heated in a neutral atmosphere to a pre-determined temperature, hardened in a hardening furnace at a specific temperature, quenched in circulating hot oil, tempered at another specific temperature, and then shot-peened using 110 shot size at an ALMEN intensity of 0.004 to 0.006 on a A strip using a standard No. 2 gauge.

United States Patent 11 1 1111 3,903,761

Runton Sept. 9, 1975 [541 PROCESS FOR THE MANUFACTURE OF 2,638,019 5/1953 Stellin 76/101 D DRIVER BITS 2,656,739 10/1953 Mansfield. 76/101 R 3,133,568 9/1964 Reed 76/101 R X Inventor: Leslie Runton, Canton, Mass- 3,211,199 10/1965 Reed 76/101 R x [73] Assignee: Phillips Screw Company, Natick,

Mass Primary bxamtnerHarr1son L. Hmson Attorney, Agent, or FirmWatson Cole Grindle & [22] Filed: Nov. 27, 1973 Watson [21] Appl. No.: 419,296

Related US. Application Data HEAT J TREATMENT 5 7 ABSTRACT A greatly strengthened driver bit is formed having a pear-shaped" cross-section and a grain structure that conforms to the external bit configuration. The driver bit is initially formed by hot-forging in an impact press; pre-heated in a neutral atmosphere to a predetermined temperature, hardened in a hardening furnace at a specific temperature, quenched in circulating hot oil, tempered at another specific temperature, and then shot-peened using 1 10 shot size at an ALMEN intensity of 0.004 to 0.006 on a A strip using a standard No. 2 gauge.

10 Claims, 11 Drawing Figures SHAPED 81 GROOVED BLANK PUNCH PRESS INDUCTION HEATING FLASH REMOVAL PREHEAT HARDENING FURNACE QUENCH (OIL) TEM PER SHOT PEENING PATENTED 75 SHEET 1 gr 2 INVENTOR LESLIE A. RUNTON Fi h m? ATTORNEYS PATENTEU SEP 91975 SHEET 2 BF 2 D G E N V l A w %M v e G K EE 0 T NE H R W NG RH M A M C E N P E E A L N R H E VN E L H@ E D E M E D C H R R U E P E C 8 P A Q T T DI UU A H O A PD L H w W F S fl. m M T A E R T FIG. 3

INVENTOR FIG 4 LESLIE A. RUNTON BY ym M ATTORNEYS PROCESS FOR THE M'ANUFACTURE' OF DRIVER .BITS 1 This is-a continuation'of application Ser. No. 184,699 filed Sept. 28, l97=l and now abandoned. a r: v f

This invention relates to a driver. bit and, a process for its manufacture and, more particularly, a drivers bit for a recess of the cruciform type and a hot forging process for forming the driver bit to eliminate-highly stressed areas by providing a specially shaped cross sectionzand a contoured grain structure. conforming'to the external outline ofthe bit.. 1

Normally driver bits are: made from hexagonal steel blank stock and have ribs which are roughly machined and then swaged by cold pressinglor coined into a final shape. Prior art driver'bits; evenwhen they have been properly heat treated and suitablynstress-:relieved,. are endowed with highly stressed areas that fail under duress. Such driver bits have been particularly unsuitable when used with air operated impact drivers which are set at high torque levels since the stresses imposed on the driver bit under such conditions creates high stress levels which are sufficient to break the drive'r 'bits in a very short time'thereby resulting in'co'ns'id'erable downtime on the'ass'embly line. i

Extensive testing of these prior art'driver bits has indicated that the breaks in the'bits' have occurred at the juncture of the ribsand the bit body' or in the ribs themselves; the stresses bein'g introduced in the forming process. It is, therefore, a primary object of this invention to eliminate such highly stressed areas by form ing the driver bit by a process that includes hot-forge shaping of the bit member.

Another object of the invention is to provide driver bit of the type specified which is suitably stress relieved to withstand the high torque levels developed bysuch devices as air operated impact drivers.

A further object of the invention is to provide a process for economically producing driver bits of the type specified having greatly increased durability and opertiling life. I, w e g The inventive process for the manufacture of driver bits eliminates highly stressed areas by providing a specially shaped cross-section and a grain' structure in the steel that compliments the external bit contour at the areas of the greatest loading forces when the driver bit is in use. The ribs are supported by a contoured platform to provide an integral structure having the strength to withstand the shocks received under severe impact use. I

It is well known in the art that hot. forging of steel, when properly controlled, will materially increase the total strength of steel parts. The process of this invention uses this method. An important feature of the invention is the use of an electric induction heater to induce a heat band on the partially shaped end portion of a steel blank. A steel die located in the hammer of a punch press and formed into a female configuration of the cruciform recess required hits the hot tip of the blank and forces the hot metal up into the hollow part of the female die. A lower die holds the blank and may be of hexagonal shape, but is relieved at the top so that at the moment of forging, both the female die on the hammer and the relieved portionof the lower die are filled with metal from the blank: This forging operation is designed to produce a pear-shaped cross-sectional configuration of the driver bit head.

The-excess flash material is then removed from the bit; the bit is then stress relieved and heat treated to providethe necessary strength. The heat treating process begins with warming of the bits to a predetermined temperature'for a set period of time; then immediately inserting the bits into a hardening furnace which is maintained at a'predetermined temperature until the driver bits have attained that temperature; the driver bits are then quenched in oil at a pre-selected temperature and are'left in the oil until they reach the temperature of the quenching oil. The driver bits are then im- 'rnediately tempered at an additional pre-selected tem perature in an atmosphere furnace to a given Rockwell hardness. The tempered bits are then shot-peened with a selected shot size at a selected intensity based on the Alman system of measurement to complete the manufacture' of the'driver bit.

Sections of the manufactured driver bits, when etched in acid, will show a grain structure that is novel in the art of driver bit manufacturing. The grain flows up the stemof the bit in parallel lines and in the region of the driver head swells out in orderly sweeping lines to conform to the general shape of the ribs and rib supporting platform. This is in contradistinction to norrnally produced commercial bits which only show parallel lines of grains'tructure. Such prior art commercial bits, no matter from what steel they are manufactured and processed, when tested in a standard torsion or fa tigue machine only come within approximately 10% of the life-to-destruction time which driving bits manufactured in accordance with the principles of this invention achieve.

Driver bits manufactured in accordance with the principles of this invention have been tested on automobile assembly lines and have lasted an average assembly of 400 cars when used in impact guns which were set to a torque of 40 pounds for a No. 4 size driving bit in a cruciform shape.

The process steps of heat treating and shot-peening are per se old; however, when misused produce poor vention will be apparent to those skilled in the art from the following description of the process and of the driver bit in accordance with the accompanying drawings wherein:

FIG. IA is a side elevational view of the blank from which the driver bit is manufactured showing in phantom the shape of the finished head and the portions of the forming and heading dies;

FIG. 1B is a side elevational view showing a completely manufactured driver bit;

FIG. 1C is a plan view of the top of a completed driver bit;

FIG. 1D is a section of a wing;

FIG. IE is a side elevation of the driver bit head;

FIG. 1F is an additional side elevational view taken from a different position of the driver head;

FIG. 1G and FIG. 1H illustrate two representative configurations of the driver point;

FIG. 2 is a sectional view of a typical driver bit illustrating the specially formed grain structure;

FIG. 3 is a flow chart of the steps involved in the process for manufacturing the driver bit, and

FIG. 4 illustrates the die members and induction coil used in the hot forging of the die blank.

which is supported by angled shoulder portion 28 on the finished blank 12. Angled portions 29 extend at approximately 40 (il) from the normal to the surface of blank 12. Platform 26 is approximately 5/64 of an A preferred form ofa blank from which the driver bit 5 inch in height and head portion 22 is approximately /2 is to be formed is illustrated in FIG. 1A. Blank 12 is mai h i di at h l f Rib 24 f a r di chined from hexagonal bar Stock to have reduced ncck 30 of0.03 to 0.04 inches with the upper surface of platperhen 14 extehdmg from the upper Surfeee 9f the form 26. The total length of blank 12 is l-5/16 inch blank and, teeth 16 formed in the lower shank portion plus or minus /1 0f the biaiik which serve to P v a meiiiis for holding i The shape of ribs 24 is better illustrated in FIG. 1C. the finished driver blank Within ltS ZISSOClZItCd tOOl. are arranged in the shape of a cruciforn and Forming dic Position i8 and heading die Position 20 angled at 90 with respect to one another. Angles C and are illustrated in phantom to lndlcate the relatlonshlp E are f Qutter angles i h plans f h illi Cut of the forging i members in producing the P formed by the milling angle H (reference FIG. 1F) and shaped head portion of the driver bit. Reduced neck th ff t angles U and W, portion 14 has tap r d Side u fa Which are FIG. 1B is a cross-section indicating angle S and S (:30') with respect to the surface of blank 12. Neck 14 which are measured in a plane parallel to h Cent is approximately 0.360 lnch to 0.370 lnch in length. line f two adjacent ribs at the G plane and l l to Blank 12 is preferably composed of the following elethe |Onghudhm1 axis f the workpiece 0 mems FIG. 1E lllustrates a slde vlew of head portion 22 ll- 0 .65; Mn 0.50; Si 1.10; v .20; Mo .50; Balance Fe. luetrming the angles D, dimension F and Plane Although the foregoing silieo-manganese tool steel is 1F is iii'icihcr Sidc cicvatioiiai View of hcaci P preferred, the following alternate steel alloy may also tioii 22 illustrating angle H which is measured in a Vertibe used. especially in those instances where it is desired 25 cal Piaiic through the ioiigitudii'iai axis of the workpiece to improve the performance of the driver bit under high at to the center him of the ribs at the G P and temperature conditions. This steel has a high silicon iii'igics U and W which are measured iii the H Piiihc, content with tungsten added. The tungsten also inch is a plane passing through the H angle at 45 to creases the toughness of the driver bit as well as its perhfi G plane Center line of the ribs.

4 tmmmLc high temperatures FIGS. 10 and 1H are top vlews of two preferred em- C .50; Mn 0.25; Si 0.75; Cr 1.3; W 2.50; Z 0.20; bodl ments of the rlb forms whlch may be cut on head Balance Fe porno The finished shape of the driver bit is shown in FIG. Table 1 lists the dimensions and tolerances for the 1B and includes shaped head portion 22 which includes various angles and dimensions indicated in FIGS. ribs 24 extending the height of the head to platform 26 1C-1H. inclusive.

TABLE 1 +15 +30 +15 400 POINT 00 00 00 -30 TMEO DRIVER SIZE B C D E F G H K R 0 .0280 .0175 036 .0010 .004 .0265 .0165 .035 .0013 .003 1 .0438 46()( 1 .0275 .055 700 .0016 .005 .0423 .0265 .054 .0000 .004 2 .0670 .0390 .096 .0045 .012 .0655 .0370 .094 .0001 .006 3F .0990 .0520 .156 545 .0094 .014 .0980 .0510 154 .0043 .008 3T .1020 4600 2600 .0540 .156 .0096 .014 .1000 .0530 154 .0054 .008 (PRE- FERRED) 4F .1490 .0790 .204 .0130 .020 .1480 5615 .0780 .202 .0093 .014 4T .1520 .0820 .204 .0131 .020 (PRE- FERRED) .1500 .0800 .202 .0051 .014 5F .2360 .0890 1 .316 700 .0426 .045 .2360 .0870 314 .0362 .035 5'1 PRlil-ER RED) +10 +30 V +l Point -00 -00 -0 DRIVER SIZE 5' s1 u w X Y Z 0 22 200 423 745 1 142 1242 2 140 1008 31" 17 204 300 620 143 845 3'1 14 1' 845 10 (PRE- FliRRliD) FIGv 2 is a cross-sectional view along a diameter of the head portion taken through two ribs which illustrates the grain structure. The process for manufacturing the driver bit insures that the grain follows the ex ternal shape of the driver to considerably enhance its strength. The grain in metal is similar to the grain in wood or that of stone in which the structure is weaker across the grain and stronger with the grain. Once the grain is cut into, the driver bit will tend to crack along with the grain. The grain structure shown in FIG. 2 eliminates this possibility and contributes greatly to the increased performance and reliability of the driver bit.

As shown in FIG. 2 the grain flows up the stem in parallel lines and under the driver head swells out in orderly sweeping lines nearly to the edge of the bit. As

mentioned previously, normal commercial bits only show parallel lines of grain structure. The grain structure is induced in the metal by the shape of the dies and the hot forging operation which will be described more fully hereinafter.

The steps involved in the process of manufacturing the greatly improved driver bit according to this invention are shown in flow chart form in FIG. 3. A hexagonal bar stock of the type of material previously mentioned herein is machined in accordance with FIG. 1A

on an automatic lathe and then inserted into a lower (heading) die of a hot-forging punch press. Heat is applied by induction heating to form a variable heat band at the upper tip of the blank. The heating is timed to last approximately 7V2 seconds and at the critical moment of impact by the forming die the temperature developed in the blank enables the alloy to flow and produce the desired grain structure in the driver bit.

The flash is then cut off the forged driver bit either on a lathe or ground off by hand.

The heat treatment involves a number of steps starting with the warming of the bit in a neutral atmosphere at 800 F. for one hour. The driver bits then are placed in a hardening furnace which is maintained at approximately l640 F. and when the bits attain or are stabilized at the hardening furnace temperature they are quenched in circulating hot oil at l50 F. The driver bits are left in the circulating quenching oil until they attain the 150 F. temperature thereof.

The bits are then immediately tempered at 450 F. in an atmosphere furnace to a Rockwell C scale of about 50.

'lhe heat treatment for the driver bits will to some extent depend upon the material of the blank from which they are manufactured. The foregoing description of the heat treatment process applies to the firstmentioned silico-manganese steel. The alternate type of steel suggested above requires a hardening procedure which involves the pre-heating of the driver bits slowly to l250 F.; the rapid heating of the driver bits to l675l 725 F. at which temperature the driver bits are held for only a sufficient enough time to evenly distribute the temperature at about l685 F.; the driver bits are then quenched in circulating oil at 150 F. and are then tempered at 450 F. to a Rockwell C scale of about 58.

After the heat treating steps, the driver bits are shotpeened in standard equipment as used by commercial shot-peening firms, using l 10 shot size and an ALMEN intensity of 0.004 to 0.006 on an A strip using standard Number 2 gauge as is commercially done in the trade. The shot-peening process has been described in SAE Manual on shot peening, AMS 2430 and MIL S- l 3 l 65 A.

Too much shot-peening is injurious to the desired result. The shot-peening indents the skin of the material and relieves any stresses that may have been induced by the earlier processes. With a more elastic skin produced by the shot-peening step, the bit can withstand more load. without cracking. The time inside the shotpeening machine is critical and is regulated by the use of the ALMEN system. Too elastic a skin produces a loss in total strength of the bit and, consequently, only enough shot-peening to relieve stresses is required.

Similarly, too much time in the hardening furnace after the bits have reached the desired temperature will result in decarburization which, of course, should be prevented.

The hot forging die and the induction heating electrodes are shown in FIG. 4. Driver bit blank 12 is inserted into heading die member 40 which includes piston 42 for ejecting the forged blank from the die structure. Induction heating electrodes 44 are provided to heat the tip of the blank to approximately 1325 F. The heat induced at the tip of the blank is conducted into the more massive shank of the blank and attains a temperature of approximately 700 F. at the shank just below the tip. The induction coil is moved up and down in a cycle which is approximately 7 seconds to induce the proper current action in the tip of the blank prior to impacting the blank to form the head portion as described above. The temperatures of the tip are maintained within +25 or 25 F. The forming die member 46 is caused to impact the blank to form the head and provide the preferred grain structure described above.

A timing device when used with a 10 kilowatt R. F. generator and set for 7 /2 seconds at 460 kilocycles with a plate voltage of 6. and DC. amps at l.6, provides the heat necessary to form the head portion as described above.

Forming die member 46 is formed into a female configuration of the cruciform recess which is desired and as it impacts with the hot tip of the blank hot metal is forced up into the hollow part of the female die. The

heading die member 40 may be hexagonal in shape, but is relieved at its top portion so that at the moment of impact, not only is the recess in the forming die filled with metal, but the relieved portion of the heading die also becomes filled with metal. The configuration of the heading and forming dies provides the pear-shape of the head portion.

Although a preferred method of manufacturing the driver bit disclosed herein has been set forth in such detail as to facilitate reproduction by those skilled in the art, such description is to be considered illustrative rather than limiting, for the method, and the driver bit itself, may be altered by the substitution of equivalents without departing from the fundamental concepts and the spirit of the invention. These equivalents could be the substitution of a three wing configuration in place of the cruciform shape and the substitution of other wing shapes not radially arranged.

What is claimed is:

l. A method for the manufacture of driver bits, comprising the steps of:

a heating the end portion of a steel alloy blank to be formed into the head portion of the driver bit to substantially that temperature enabling said head portion to flow under pressure;

b. forging the head portion by impacting a forming die member into a holding die member containing the steel alloy blank whereby the grain contours of said alloy in said head portion substantially conform to the external configuration thereof and the grain contours of said alloy in the region adjacent said head portion substantially conform to the external configuration thereof;

c. hardening and tempering the forged driver bit; and

d. shot-peening said driver bit to relieve stresses and to provide an elastic skin surface.

2. A method as in claim 1 further comprising the step of oscillating said steel alloy blank along its longitudinal axis during said step of heating.

3. A method as in claim 2 wherein the frequency of said oscillation is one cycle and said step of heating is approximately 7 /2 seconds.

4. A method as in claim 1 wherein said end portion is pre-formed to have a reduced neck portion extending from said steel blank and said heating is applied to said reduced neck portion.

5. A method as in claim 1 wherein said steps of heat ing and forging are performed by a punch press having an induction heating element mounted thereon.

6. A method as in claim 1 wherein saidsteel alloy blank is an alloy selected from the group consisting of an alloy of 0.65% C, 0.50% Mn, 1.10% Si, 0.20% V, 0.50% M0, the balance Fe and 0.50% C, 0.25% Mn, 0.75% Si, 1.3% Cr, 2.50% W, 0.20% Z, the balance Fe; and said temperature is in the range of l300 to 1350 F.

7. The method according to claim 6 wherein said steel alloy is the last mentioned alloy of said group and said step of hardening and tempering the driver bit includes the additional steps of:

a. pre-heating said driver bit to a temperature of substantially 1250 F.; Y

b. heating said driver bit to a temperature between the range of 1675 to 1725 C.;

c. stabilizing said driver bit at a temperature of approximately 1685 F.;

d. quenching said driver bit in circulating oil at a temperature of approximately F. until it has cooled to the temperature of the oil; and

e. tempering said driver bit at approximately 450 F.

to a Rockwell C scale of substantially 58.

8. A method as in claim 7 wherein said step of shotpeening includes the use of 1 10 shot size at an Almen intensity of 0.004 to 0.006 on an A strip using a No 2 standard gauge.

9. The method according to claim 6 wherein said steel alloy is the first mentioned alloy of said group and the step of hardening and tempering the driver bit includes the additional steps of: I

a. heating the driver bit at a temperature of substantially 800 F. for approximately one hour,

, b. hardening said driver bit until it attains a temperature of approximately 1640 F., i

c. quenching said driver bit in circulating oil at a temperature of substantially 150 F. until it has cooled to the temperature of the oil, and

d. tempering said driver bit at 450 F. to a Rockwell C scale of 50.

10. The method according to claim 9 wherein the step of shot-peening includes the use of 1 10 shot size at an ALMEN intensity of 0.004 to 0.006 on an A strip using a No. 2 Standard gauge. 

1. A method for the manufacture of driver bits, comprising the steps of: a. heating the end portion of a steel alloy blank to be formed into the head portion of the driver bit to substantially that temperature enabling said head portion to flow under pressure; b. forging the head portion by impacting a forming die member into a holding die member containing the steel alloy blank whereby the grain contours of said alloy in said head portion substantially conform to the external configuration thereof and the grain contours of said alloy in the region adjacent said head portion substantially conform to the external configuration thereof; c. hardening and tempering the forged driver bit; and d. shot-peening said driver bit to relieve stresses and to provide an elastic skin surface.
 2. A method as in claim 1 further comprising the step of oscillating said steel alloy blank along its longitudinal axis during said step of heating.
 3. A method as in claim 2 wherein the frequency of said oscillation is one cycle and said step of heating is approximately 7 1/2 seconds.
 4. A method as in claim 1 wherein said end portion is pre-formed to have a reduced neck portion extending from said steel blank and said heating is applied to said reduced neck portion.
 5. A method as in claim 1 wherein said steps of heating and forging are performed by a punch press having an induction heating element mounted thereon.
 6. A method as in claim 1 wherein said steel alloy blank is an alloy selected from the group consisting of an alloy of 0.65% C, 0.50% Mn, 1.10% Si, 0.20% V, 0.50% Mo, the balance Fe and 0.50% C, 0.25% Mn, 0.75% Si, 1.3% Cr, 2.50% W, 0.20% Z, the balance Fe; and said temperature is in the range of 1300* to 1350* F.
 7. The method according to claim 6 wherein said steel alloy is the last mentioned alloy of said group and said step of hardening and tempering the driver bit includes the additional steps of: a. pre-heating said driver bit to a temperature of substantially 1250* F.; b. heating said driver bit to a temperature between the range of 1675* to 1725* C.; c. stabilizing said driver bit at a temperature of approximately 1685* F.; d. quenching said driver bit in circulating oil at a temperature of approximately 150* F. until it has cooled to the temperature of the oil; and e. tempering said driver bit at approximately 450* F. to a Rockwell C scale of substantially
 58. 8. A method as in claim 7 wherein said step of shot-peening includes the use of 110 shot size at an Almen intensity of 0.004 to 0.006 on an A strip using a No. 2 standard gauge.
 9. The method according to claim 6 wherein said steel alloy is the first mentioned alloy of said group and the step of hardening and tempering the driver bit includes the additional steps of: a. heating the driver bit at a temperature of substantially 800* F. for approximately one hour, b. hardening said driver bit until it attains a temperature of approximately 1640* F., c. quenching said driver bit in circulating oil at a temperature of substantially 150* F. until it has cooled to the temperature of the oil, and d. tempering said driveR bit at 450* F. to a Rockwell C scale of
 50. 10. The method according to claim 9 wherein the step of shot-peening includes the use of 110 shot size at an ALMEN intensity of 0.004 to 0.006 on an A strip using a No. 2 Standard gauge. 